Users who engage in video editing on a computing device may combine and customize various multimedia layers into a composition schema, which may include video, audio, graphic and text layers, etc. When using a browser for video editing over the Internet, multimedia assets are stored externally and these sources (e.g., remote servers and computing devices) must send data asynchronously to the browser in order for the user to access multimedia not stored on their computing device. The browser-based video composition has the ability pull external resources from the Internet and manage these asynchronous tasks in order to successfully playback a video composition in the browser. However, there is a need to sync all external resources of each multimedia layer.